This invention relates to a temperature sensor. The invention is particularly, but not exclusively, pertinent to a thermostatic sensor which is operative to cut off or reduce the heating effect of a heat producing device when the sensor detects a temperature at or above a predetermined temperature, and which may be operative to restore the heating effect of the heat producing device when the sensor detects a temperature below the predetermined temperature.
The invention has been primarily devised for use with an electrical heat producing device such as a heating tape to cut off or reduce the power supply to the heating tape when a temperature at or above the predetermined temperature is sensed, although the sensor may be used in many other applications, for example to restrict the supply of fuel to a heat producing device comprising a fuel burner, when the temperature detected is at or above the predetermined temperature or merely to give warning when the predetermined temperature has been reached.
In a heating tape, a conductor (or conductors) extends along the length of the tape. An electrical current is passed through the conductor and, due to the resistance of the conductor, heating occurs. Such heating tapes have many applications such as in preventing the freezing of chemicals in an exposed pipe or duct, around which such heating tape may be wound, or to maintain the temperature of a chemical as the chemical flows from one location to another along a pipe or duct.
Another use is to heat a chemical, in a container around which the tape is wound, to a specific temperature.
It will be appreciated that many chemicals are temperature unstable, that is, the chemical must be kept at or close to a particular temperature for the chemical to be stable. It is important in many applications, for the heating effect of the heating tape to be carefully controlled. Furthermore, it is important to ensure that the heating tape itself is not raised to a temperature above its design limits, when damage to the heating tape could occur. For example, in common types of heating tape, the or each conductor is encased in a rubber or rubbery material to give the tape flexibility and durability as well as protecting the conductor(s) from any adverse environmental conditions. If the tape overheats, the casing material could deteriorate.
It is current practice to monitor the temperature of the heating tape when in use or the chemical being heated at spaced positions but a compromise has to be made between monitoring the temperature at closely spaced positions when a large number of temperature monitors need to be provided, thereby increasing costs, and monitoring the temperature at more widely spaced positions, thereby minimising costs. Of course the former system of monitoring, i.e. using a large number of monitors is the more desirable, allowing for closer monitoring of the temperature, where costs permit.
It would be preferred for the temperature to be monitored along the entire length of the tape without having to provide a large number of temperature monitors.